the Importance of Soil Bill Hunt, Ph.D., PE, D.WRE Associate - PowerPoint PPT Presentation

MN Clean Water Summit – UMN Arboretum, MN – 13Sep12 Low Impact Development and the Importance of Soil Bill Hunt, Ph.D., PE, D.WRE Associate Professor & Extension Specialist North Carolina State University www.bae.ncsu.edu/stormwater

The Real Reason I’m Happy to Be Here www.bae.ncsu.edu/stormwater

Outline • Soil Importance on Defining the Target Condition • Underlying Soils & Infiltration by SCMs • Utilizing Soil / Media to Sequester/ Mitigate Pollutants – Phosphorus, Temperature, + MediaDepths • Minimizing Compaction Impacts to Maximize Infiltration www.bae.ncsu.edu/stormwater

Low Impact Development • Reduce impervious surfaces • Retain runoff on-site • Promoting infiltration and evapotranspiration • Soils were recognized by the “Founding Fathers” www.bae.ncsu.edu/stormwater

Early on… LID “First Step” • How to Lay Out your site? • Where to location your practices? • Is ideally based on… www.bae.ncsu.edu/stormwater www.bae.ncsu.edu/stormwat er

Courtesy of Todd Houser, Cuyahoga S&W Your Soils! www.bae.ncsu.edu/stormwater

e.g., Cuyahoga County Soils & LID • Loamy Sand & Sand (5.8%) – Infiltration, if well drained – Wet or dry BMP depending on drainage class • Well Drained Soils (12.6%) – Dry BMPs • Moderately Well Drained (11.2%) – 1.5 - 3 ft. November to May most years – Shallower – Wet / ( 4 22 – Deeper – Dry with Liner • Somewhat – Very Poorly Drained (76.2%) – 0.5 – 1 ft. November to June most years – Wet BMPS KSU • Slippage Prone (5.8%) – Stay Away Courtesy of Todd Houser, Cuyahoga S&W • Urban Complexes (49.9%) – Highly Variable www.bae.ncsu.edu/stormwater

Goals of Low Impact Development • Reduce impervious surfaces • Retain runoff on-site • Promoting infiltration and evapotranspiration • Replicating pre-development hydrologic conditions as closely as possible - Davis, 2005 Amounts of Each – Depending upon Underlying Soil www.bae.ncsu.edu/stormwater

Primary Goal of LID Design each development site to protect, or restore, the natural hydrology of the site so that the overall integrity of the watershed is protected. This is done by creating a “ hydrologically ” functional landscape. www.bae.ncsu.edu/stormwater

What is the Target Condition? • In North Carolina, Coweeta – Coweeta is a US Forest Service Research Station www.bae.ncsu.edu/stormwater

Establishing Target Condition • Coweeta Hydrologic Laboratory – Forested Mountain Watersheds – Longest Term Hydrologic Record (Runoff, Infiltration, and ET) in the World for a forest site • Records used for this study were 37 and 50 years old – Rain Shed Mountain Region • Annual Precipitation in excess of 1500 mm (60 inches) • Drawback: Coweeta Wetter than any major city in NC – Data From Swift, LW, G.B. Cunningham, J.E. Douglass. 1987. “Climatology and Hydrology.” Forest Hydrology and Ecology at Coweeta . Eds: W.T. Swank and D.A. Crossley. Springer Verlag. New York, NY, pp 35-57. www.bae.ncsu.edu/stormwater

Establishing Target Condition Annual Hydrologic Fate Average Amount Percent of Total Precipitation Precipitation 1770 mm (70 in) 100% Runoff 80 mm (3 in) 5% Evapotranspiration 890 mm (35 in) 50% Infiltration 800 mm (31 in) 45% Shallow Interflow 770 mm (30 in) 44% Deep Seepage 30 mm (1 in) 2% All values rounded to the nearest 10 mm or 1 in. Infiltration is the sum of Shallow Interflow and Deep Seepage www.bae.ncsu.edu/stormwater

Santee Experimental Forest (Coastal Plain South Carolina) Evapo- Infiltration + transpiration Runoff Experimental Data 77% 23% (Amatya et al., 2006)  Coastal plain region, undisturbed woods, sandy soils  30+ years of experimental data www.bae.ncsu.edu/stormwater

Why the Difference? • Sandier Soil Systems + flatter landscapes + higher water table systems = MORE ET • Underlying SOILS! • Soils impact what your HYDROLOGIC TARGET CONDITION is www.bae.ncsu.edu/stormwater

Example of Target Condition Variation Landscape Detention: NC North Carolina Grassed Cell 140 NC Grassed Cell Pavement 120 Woods B (CN 55) Woods C (CN 70) 100 Outflow Volume (m^3) Regression (CN 79) 80 60 40 20 0 0 1 2 3 4 5 6 7 Rainfall (cm) www.bae.ncsu.edu/stormwat er

So, how well do SCMs “Convert” Runoff to Infiltration? www.bae.ncsu.edu/stormwat er

Answer: It depends (in part) on Underlying Soil www.bae.ncsu.edu/stormwat er

Improving Infiltration www.bae.ncsu.edu/stormwat er

Water Balance Brown & Hunt, JEE 2011 www.bae.ncsu.edu/stormwater

Reduced Performance in Clayey in- situ Soils • Rocky Mount (sand): Upper Coastal Plain • Greensboro (clay): Piedmont • Graham: (N) loamy-clay & (S) sandy-loam Site # Events # Events w/ Media IWS Depth Monitored Outflow Depth (m) (m) RM Grass 78 5 0.9 0.6 RM Mulched 78 4 0.9 0.6 Greensboro 1 63 18 1.2 0.6 Greensboro 2 63 40 1.2 No IWS Graham (N) 40 34 0.6 0.3 Graham (S) 40 22 0.9 0.6 “We Bring Engineering to Life”

Ritter Field Stormwater Wetland (River Bend, NC) www.bae.ncsu.edu/stormwater

Runoff Reduction by Storm 10000.0 Line if 1000.0 Outflow Volume= Outflow (m3) Inflow 100.0 Volume 10.0 1.0 1.0 10.0 100.0 1000.0 10000.0 Inflow (m3) Lenhart and Hunt. JEE. 2011 www.bae.ncsu.edu/stormwater

Wetlands are not “supposed” to reduce runoff volumes this much! • Why is this wetland so “good” at infiltrating? Design Element Value Watershed Size 115 ac Wetland Size 0.34 ac Watershed Curve Number 55 Underlying Soil at Wetland Appling Fine Sand www.bae.ncsu.edu/stormwater

Ritter Field Stormwater Wetland: Why is it so (relatively) small? Design Element Value Watershed Size 115 ac Wetland Size 0.34 ac Watershed Curve Number 55 Underlying Soil at Wetland Appling Fine Sand

Determining Volume: Using NRCS Methods • NRCS Curve Number Method – SA = Volume (V) ÷ Ponding Depth Depth (D) – V = Runoff Depth (Q*) × Watershed Area (A) – Q = (P – 0.2 S) 2 ÷ (P +0.8 S) P= Precipitation Depth; S = Initial Abstraction – S = 1000/CN - 10 CN = Curve Number www.bae.ncsu.edu/stormwater

Key “Mid - term” Take Home Points • Underlying Soils impact performance of a Stormwater Control Measure – E.g., SCMs over sandy soil will infiltrate (sometimes much) more than those over clays • Underlying Soils have major factor in size of practice (& therefore cost) – Sandy Watersheds can have much smaller SCMs than Clayey Watersheds www.bae.ncsu.edu/stormwater

Watershed Soils & SCM effectiveness www.bae.ncsu.edu/stormwater

Bacteria Pollution • Stormwater is a transport mechanism for bacterial pollution • Urbanization can lead to increased pathogen loads to surface waters – Pet waste, sewer overflow, sewer leakage • Leads to 50,000 acres of Shellfish closures in NC each year. www.bae.ncsu.edu/stormwater

Charlotte Wet Pond Piedmont Clays Waters ershed ed = 48.6 6 ha CN = 75 www.bae.ncsu.edu/stormwater

Wilmington Wet Pond Coastal Plain Sands www.bae.ncsu.edu/stormwater

Charlotte (Clay) Wet Pond – E.Coli www.bae.ncsu.edu/stormwater Hathaway and Hunt. JIDE. 2012

Sand Underlying Soil Pond – E.Coli www.bae.ncsu.edu/stormwater Hathaway and Hunt. JIDE. 2012

Why? • Pathogen Indicator Species “travel” (in part) on sediment • Coarser sediment = better trapping efficiency for TSS – And therefore for E.Coli www.bae.ncsu.edu/stormwater Hathaway and Hunt. JIDE. 2012

Fill Soils/ Media & SCM Effectiveness www.bae.ncsu.edu/stormwater

Greensboro Bioretention www.bae.ncsu.edu/stormwater

TP Removal/Sequestration Greensboro 3 Mass (Kg) 2.5 2 In 1.5 Out 1 0.5 0 TN NO3-N TKN TP Hunt et al. JIDE. 2006 www.bae.ncsu.edu/stormwater

Chapel Hill Cell, C1 STP/WS = 0.14 Conventional Drainage “We Bring Engineering to Life”

TP Removal/ Sequestration Chapel Hill 0.8 0.6 Mass In 0.4 (Kg) Out 0.2 0 TN NO3-N TKN TP Hunt et al. JIDE. 2006 www.bae.ncsu.edu/stormwater

Results of Early Research • Relationship between P-Index (Soil Test P) and TP outflow load. Greensboro Chapel Hill TP +240% - 65% P-Index 85-100 4-12 P-Index 50-100: High P-Index 0-25: Low (Hunt 2003) Hunt et al. JIDE. 2006 www.bae.ncsu.edu/stormwater

Blame it on the Media… Phosphorus Index (P- Index) is a measure of how much phosphorus is already in the soil media. Low P-Index: Can capture more phosphorus High P-Index: Soil is “saturated” with Very High: > 100 High: 50-100 phosphorus Medium 25-50 Low: 0-25 www.bae.ncsu.edu/stormwater

Enter… the NC “Standard” Fill Media • 85% Sand • 10% Fines (Silt + Clay) • 5% Organic Matter • + Low P-Index – 10 to 30 • Time to test it… www.bae.ncsu.edu/stormwater

Mecklenburg Co. Hal Marshall Bioretention Cell (2004-2006) Soil – 80% Mason Sand – 20% Fines + Compost – P-Index = 6 – 4 ft (1.2 m) Depth www.bae.ncsu.edu/stormwater

TP - Charlotte, NC (2004-2006) Concentration Red. = 31%; Load Reduct. ≈ 50% 0.8 0.7 TP-In 0.6 [TP] in mg/L TP-Out 0.5 0.4 0.3 0.2 0.1 0.0 1/1/04 7/1/04 12/30/04 6/30/05 12/29/05 Date Hunt et al., JEE. 2008 www.bae.ncsu.edu/stormwater